US4629632A - Production of magnetic recording media - Google Patents

Production of magnetic recording media Download PDF

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Publication number
US4629632A
US4629632A US06/759,235 US75923585A US4629632A US 4629632 A US4629632 A US 4629632A US 75923585 A US75923585 A US 75923585A US 4629632 A US4629632 A US 4629632A
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US
United States
Prior art keywords
layer
double bonds
weight
component
adhesion
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Expired - Fee Related
Application number
US06/759,235
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English (en)
Inventor
Werner Balz
Jenoe Kovacs
Hilmar Lechner
Dieter Schaefer
Ingolf Buethe
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Emtec Magnetics GmbH
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BASF SE
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Assigned to BASF AKTIENGESELLSCHAFT reassignment BASF AKTIENGESELLSCHAFT ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: BALZ, WERNER, BUETHE, INGOLF, KOVACS, JENOE, LECHNER, HILMAR, SCHAEFER, DIETER
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Publication of US4629632A publication Critical patent/US4629632A/en
Assigned to EMTEC MAGNETICS GMBH reassignment EMTEC MAGNETICS GMBH CHANGE OF NAME (SEE DOCUMENT FOR DETAILS). Assignors: BASF MAGNETICS GMBH
Anticipated expiration legal-status Critical
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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73923—Organic polymer substrates

Definitions

  • the present invention relates to a process for the production of layer-type magnetic recording media by applying a dispersion of magnetically anisotropic material in a binder solution onto a flexible plastic base provided with an adhesion-promoting layer and then solidifying the magnetic layer, wherein the adhesion-promoting layer consists a radiation-curable aqueous dispersion of a polymer.
  • the magnetic layer is required to possess uniform mechanical properties, a lack of adequate solvent resistance is troublesome particularly in the case of the adhesion-promoting intermediate layers which are intended to fix the magnetic layer on the base film and are usually extremely thin. Moreover, in most of the processes for the production of these intermediate layers, the large amounts of organic solvents used for producing the thin layers present problems.
  • layer-type magnetic recording media which meet the requirements set can be produced by applying a dispersion or magnetically anisotropic material in a binder solution onto a flexible plastic base provided with an adhesion-promoting intermediate layer and then solidifying the magnetic layer, if the adhesion-promoting intermediate layer is obtained by applying a radiation-curable aqueous dispersion of a polymer onto the flexible plastic base, drying the layer and then crosslinking it with UV light.
  • Suitable radiation-curable aqueous dispersions of polymers are prepolymers which are dispersed in water, contain from 0.01 to 1.0 mole of polymerizable C--C double bonds per 100 g of prepolymer, and have a mean molecular weight of not less than 350 and a viscosity of not less than 600 cP at 23° C.
  • Preferred compounds are polymerizable polyesters which contain C--C double bonds and have an acid number of not more than 10, polymerizable polyethers containing C--C double bonds, hydroxyl-containing reaction products of a polyepoxide containing not less than two epoxide groups per molecule with one or more ⁇ , ⁇ -ethylenically unsaturated carboxylic acids, polyurethane (meth)acrylates, and acrylic copolymers containing ⁇ , ⁇ -ethylenically unsaturated acyl radicals.
  • an aliphatic or araliphatic polyether which is obtained by reacting dihydric and/or polyhydric alcohols, which are also mentioned under 1., with various amounts of ethylene oxide and/or propylene oxide, and some or all of whose free hydroxyl groups are etherified with ethylenically unsaturated alcohols, e.g. allyl alcohol, methyallyl alcohol, crotyl alcohol or cinnamyl alcohol, and/or esterified with ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acids, as mentioned under 1.,
  • an unsaturated hydroxyl-containing compound which can be prepared by reacting a polyepoxide having on average not less than two epoxide groups per molecule, for example polyglycidyl ethers of polyhydric alcohols, as also mentioned under 1., polyglycidyl ethers of polyhydric phenols, such as bisphenol A, glycidyl esters of polybasic carboxylic acids, as also mentioned under 1., other glycidyl compounds, e.g. triglycidyl isocyanurate, and/or epoxidized natural or synthetic oils, with ⁇ , ⁇ -ethylenically unsaturated carboxylic acids as also mentioned under 1.,
  • a polyurethane which may or may not contain urea groups and can be prepared from aliphatic and/or aromatic polyisocyanates, e.g. tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, toluylene diisocyanate, naphthylene diisocyanate or 4,4'-diphenyl ether diisocyanate, any dimers or trimers derived from these, and their reaction products with minor amounts of compounds possessing active hydrogen, for example polyhydric alcohols, which are also mentioned under 1., polyfunctional amines and/or amino alcohols, by reaction with hydroxyl-containing (meth)acrylates, such as hydroxypropyl (meth)acrylate and/or butanediol mono(meth)acrylate, and
  • a polymer which can be obtained by introducing ⁇ , ⁇ -ethylenically unsaturated acyl radicals, which are derived from, for example, the ⁇ , ⁇ -ethylenically unsaturated monocarboxylic acids mentioned under 1., into acrylate copolymers, styrene/acrylate copolymers or the like which are prepared by a conventional solution polymerization method, having a content of not less than 0.02 mole of hydroxyl, carboxyl and/or epoxide groups per 100 g of substance.
  • polymeric leveling agents are added to the aqueous dispersions used for the preparation of the adhesion-promoting intermediate layer.
  • polymeric leveling agents are preferably water-soluble high molecular weight organic compounds containing polar groups, e.g. polyvinylpyrrolidone, copolymers of vinyl propionate or acetate and vinylpyrrolidone, partially hydrolyzed copolymers of acrylates and acrylonitrile, polyvinyl alcohols having various residual acetate contents, cellulose ethers, gelatin or mixtures of these substances.
  • Particularly preferred protective colloids are polyvinyl alcohol having a residual acetate content of less than 35, in particular from 5 to 30 mol % and/or a vinylpyrrolidone/vinyl propionate copolymer having a vinyl ester content of less than 35, in particular from 5 to 30, % by weight.
  • nonionic emulsifiers are relatively long-chain alcohols or phenols of various degrees of oxyethylation and/or oxypropylation (adducts containing from 4 to 50 moles of ethylene oxide and/or propylene oxide). Combinations of the above protective colloids with emulsifiers of this type are particularly advantageous since they give more finely divided dispersions.
  • the radiation-curable dispersions furthermore contain conventional photoinitiators which are soluble or dispersible in water and initiate polymerization under the action of light of short wavelength, in particular ultraviolet light.
  • Suitable photoinitiators are in general benzoin and its derivatives, such as benzoin methyl ether or benzoin ethyl ether, ketones, such as acetophenone, benzophenone or Mischler's ketone, and diketones, such as benzil. Dimethylhydroxyacetophenone has proven particularly useful.
  • the photoinitiators are used in an amount of 0.1 to 20, preferably from 0.5 to 10, % by weight, based on the photopolymerizable adhesion promoter. In order to accelerate the polymerization, accelerators are also used, these predominantly being tertiary amines, e.g. triethalamines and the like.
  • Advantageously used sources of light for initiating the polymerization are those which emit light having a wavelength of from 2,000 to 8,000 ⁇ and produce a sufficient proportion of light within this wavelength range, for example low pressure or high pressure mercury lamps.
  • High pressure mercury lamps have proven the most suitable for carrying out the procedure in the presence of air.
  • the aqueous dispersions intended for producing the adhesion-promoting intermediate layer are applied in the apparatuses conventionally employed for magnetic coating.
  • the application procedure can be carried out using the conventional gravure rollers or knife coaters, and a concentration of the dispersion can vary from 5 to 30%, preferably from 10 to 20%. This gives adhesion-promoting layers about 0.2-5 ⁇ m, preferably 0.5-1 ⁇ m, thick.
  • the adhesion-promoting intermediate layer has been applied onto the conventional base, in particular a film of a linear polyester, such as polyethylene terephthalate, and has been cured, the production of the magnetic recording medium is continued in a conventional manner.
  • a film of a linear polyester such as polyethylene terephthalate
  • composition and preparation of the dispersion of the magnetic materials in the dissolved or dispersed polymer binder correspond to the conventional processes.
  • Suitable binders for the dispersion of the finely divided magnetic material are those conventionally used for the production of magnetic layers, for example a nylon copolymer which is soluble in conventional solvents, a polyvinylformal, a polyurethane elastomer, mixtures of polyisocyanates and fairly high molecular weight polyhydroxy compounds or vinyl chloride polymers containing more than 60% of vinyl chloride building blocks, e.g.
  • a vinyl chloride copolymer containing one or more comonomers such as a vinyl ester of a monocarboxylic acid of 2 to 9 carbon atoms, or an ester of an aliphatic alcohol of 1 to 9 carbon atoms with an ethylenically unsaturated carboxylic acid of 3 to 5 carbon atoms, e.g.
  • Any crosslinking of the magnetic recording layer which may be required, depending on the binder system and tape properties, can be effected by reacting the polyurethanes or polyurethane binder mixtures with polyisocyanates.
  • polyisocyanates A large number of organic di-, tri- or polyisocyanates or isocyanate prepolymers having a molecular weight of 10,000, preferably from 500 to 3,000, can be used for the crosslinking.
  • Preferred polyisocyanates are those which carry more than 2 NCO groups per molecule.
  • Polyisocyanates which are based on toluylene diisocyanate, hexamethylene diisocyanate or isophorone diisocyanate and are produced by polyaddition with diols or triols or by biuret and isocyanurate formation have proven particularly useful.
  • the amount of polyisocyanate can vary greatly depending on the binder system.
  • cyclic ethers such as tetrahydrofuran or dioxane
  • cyclic ketones such as cyclohexanone
  • solvents depending on the type of binder. If polyurethanes are used, they may of course also be dissolved in other highly polar solvents, such as dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide or ethylene glycol acetate. It is also possible to mix the stated solvents with aromatics, such as toluene or xylene, and esters, such as ethyl or butyl acetate.
  • Preferred magnetic materials are finely divided acicular gamma-iron(III) oxide having a mean particle size of from 0.1 to 2 ⁇ m, in particular from 0.1 to 0.9 ⁇ m, or acicular chromium dioxide having the same particle structure as that stated for the iron oxide.
  • Other suitable materials are gamma-iron(III) oxide doped with heavy metals, in particular with cobalt, and finely divided metal alloys of iron, cobalt and/or nickel.
  • additives for improving the magnetic layer may be added to the dispersions, for example fatty acids, polycarboxylic acids, mono-, di- or polysulfonic acids or phosphoric acids, mixtures of these, esters or salts with metals of groups 1 to 4 of the Periodic Table, waxes, lecithins, silicone oils and fluorocarbons, and fillers such as carbon black, graphite, quartz flour and/or non-magnetizable powders based on silicates.
  • the total amount of such additives is less than 10% by weight, based on the magnetic layer.
  • the magnetic layer is produced in a conventional manner, the magnetic material being dispersed with the binder used and sufficient solvent in a dispersing machine, e.g. a tubular ball mill or a stirred ball mill, with the addition of dispersants and, if required, further additives.
  • a dispersing machine e.g. a tubular ball mill or a stirred ball mill
  • the advantageous binder/pigment ratio can be established by adding these to the mixture either in solid form or in the form of from 10 to 60% strength solutions or from 30 to 60% strength dispersions. It has proven advantageous to continue dispersing until an extremely fine distribution of the magnetic material is achieved, which may take from 1 to 5 days. Subsequent repeated filtering gives a completely homogeneous magnetic dispersion. Any crosslinking agents required are added to the dispersion before the coating procedure.
  • Suitable non-magnetic and non-magnetizable bases are the conventional bases, in particular films of linear polyesters, such as polyethylene terephthalate, which are in general from 4 to 200 ⁇ m, in particular from 6 to 75 ⁇ m, thick.
  • the anisotropic magnetic particles are oriented along the intended recording direction by the action of a magnetic field.
  • the magnetic layer can then be calendered and compacted on conventional apparatuses by passing it between heated and polished rollers, if necessary under pressure, at from 50° to 100° C., preferably from 60° to 80° C.
  • the thickness of the magnetic layer is in general from 3 to 20 ⁇ m, preferably from 4 to 15 ⁇ m.
  • the magnetic recording media produced according to the invention and possessing the advantageous adhesion-promoting intermediate layer exhibit substantially improved adhesion of the magnetic layer to the base compared with the prior art magnetic recording media.
  • the radiation-crosslinked adhesion-promoting layers eliminate the disadvantageous sensitivity to solvents, which was usual in the past.
  • the intermediate layers are moreover mechanically very stable, in particular scratch-resistant.
  • the novel process also results in a substantial improvement in the homogeneity of the magnetic layer, due in particular to the presence of fewer coating defects, and in the mechanical properties of the layer, especially the durability and the stability under high temperature and humidity conditions.
  • the dispersion was filtered and applied onto a 15 ⁇ m thick polyethylene terephthalate film using a gravure roller.
  • the water was then evaporated by means of a stream of hot air at 65° C., and the dry layer was crosslinked by means of a UV lamp (2.4 kW).
  • the thickness of the adhesion-promoting layer was 0.5 ⁇ m.
  • the dispersion for the magnetic layer was then applied.
  • a thermoplastic polyester urethane obtained from adipic acid, but
  • a further 640 parts of the stated polyester urethane solution and 100 parts of the phenoxy resin solution, 18 parts of butyl stearate, 4.5 parts of streaic acid and 400 parts of the stated solvent mixture were then added, and dispersing was continued for 24 hours.
  • the resulting dispersion was filtered under pressure through a filter having 5 ⁇ m pores and was applied, by means of a conventional knife coater, onto the polyethylene terephthalate film provided with the adhesion-promoting layer.
  • the coated film was passed through a magnetic field to orient the magnetic particles and then dried at from 60° to 80° C. After drying, the magnetic layer of the coated film was calendered and compacted by being passed twice between heated rollers at 90° C.
  • the thickness of the magnetic layer was 4 ⁇ m.
  • the adhesion-promoting effect was determined by measuring the separating force and the peeling resistance according to U. Zoll, Adhesion 1979, No. 5, pages 128-134. The results of the measurements are shown in the Table.
  • Example 1 The dispersion for the magnetic layer described in Example 1 was applied directly onto the polyethylene terephthalate film by the method described there. The separating force and peeling resistance measured are shown in the Table.
  • Example 1 The procedure described in Example 1 was followed, except that the magnetic-layered dispersion below was applied.

Landscapes

  • Paints Or Removers (AREA)
  • Magnetic Record Carriers (AREA)
  • Manufacturing Of Magnetic Record Carriers (AREA)
US06/759,235 1984-07-27 1985-07-26 Production of magnetic recording media Expired - Fee Related US4629632A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE3427683 1984-07-27
DE19843427683 DE3427683A1 (de) 1984-07-27 1984-07-27 Verfahren zur herstellung magnetischer aufzeichnungstraeger

Publications (1)

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US4629632A true US4629632A (en) 1986-12-16

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US (1) US4629632A (de)
EP (1) EP0169522B1 (de)
JP (1) JPS6185625A (de)
DE (2) DE3427683A1 (de)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3215554A (en) * 1962-01-22 1965-11-02 Gevert Photo Producten N V Subbing layer for magnetic recording materials
US4468436A (en) * 1982-12-23 1984-08-28 Fuji Photo Film Co., Ltd. Magnetic recording material

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2853921A1 (de) * 1978-12-14 1980-07-03 Basf Ag Strahlungshaertbare waessrige bindemitteldispersionen
US4511629A (en) * 1982-02-05 1985-04-16 Tdk Electronics Co., Ltd. Magnetic recording medium

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3215554A (en) * 1962-01-22 1965-11-02 Gevert Photo Producten N V Subbing layer for magnetic recording materials
US4468436A (en) * 1982-12-23 1984-08-28 Fuji Photo Film Co., Ltd. Magnetic recording material

Also Published As

Publication number Publication date
EP0169522A3 (en) 1988-06-01
DE3573346D1 (en) 1989-11-02
DE3427683A1 (de) 1986-02-06
EP0169522B1 (de) 1989-09-27
EP0169522A2 (de) 1986-01-29
JPS6185625A (ja) 1986-05-01

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